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This study applied a life cycle assessment (LCA) methodology for a comparative environmental analysis between an innovative algae resource recovery and near zero-liquid discharge potable reuse system (i.e., the main system) versus a conventional potable reuse system (i.e., the benchmark system) through energy use and greenhouse gas (GHG) emissions. The objective of this study is to demonstrate that pilot-scale data coupled with LCA would provide valuable information for system optimization, integration, and improvements for the design of environmentally sustainable full-scale systems. This study also provides decision-makers valuable information regarding the energy demand and environmental impact of this innovative main system compared to a typical tried-and-true system for potable water reuse. The main system consists of a novel algal-based wastewater treatment coupled with a dual forward osmosis and seawater reverse osmosis (Algal FO-SWRO) membranes system for potable water recovery and hydrothermal liquefaction (HTL) to recover biofuels and valuable nutrients from the harvested algal biomass. The benchmark system refers to the current industry standard technologies for potable water reuse and waste management including a secondary biological treatment, microfiltration (MF), brackish water reverse osmosis (BWRO), ultraviolet/advanced oxidation process (UV-AOP), and granular activated carbon (GAC), as well as anaerobic digestion for sludge treatment. Respective energy and GHG emissions of both systems were normalized and compared considering 1 m 3 of water recovered. Based on an overall water recovery of 76% designed for the benchmark system, the energy consumption totaled 4.83 kWh/m 3 , and the system was estimated to generate 2.42 kg of CO 2 equivalent/m 3 with most of the emissions coming from the biological treatment. The main system, based on an overall water recovery of 88%, was estimated to consume 4.76 kWh/m 3 and emit 1.49 kg of CO 2 eq/m 3 . The main system has high environmental resilience and can recover bioenergy and nutrients from wastewater with zero waste disposal. With the application of energy recovery devices for the HTL and the SWRO, increase in water recovery of the FO membrane, and replacement of the SWRO membrane with BWRO, the main system provides an energy-competitive and environmentally positive alternative with an energy demand of 2.57 kWh/m 3 and low GHG emissions of 0.94 kg CO 2 eq/m 3 ., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

This study developed a comprehensive techno-economic assessment (TEA) framework to evaluate an innovative algae resource recovery and near zero-liquid discharge potable reuse system (i.e., the main system) in comparison with a conventional potable water reuse system (i.e., the benchmark system). The TEA study aims to estimate the levelized costs of water of individual units and integrated processes including secondary wastewater treatment, advanced water purification for potable reuse, and sludge treatment. This would provide decision-makers valuable information regarding the capital and operational costs of the innovative main system versus a typical potable water reuse treatment train, along with possible routes of cost optimization and improvements for the design of full-scale facilities. The main system consists of (i) a novel algal-based wastewater treatment coupled with a dual forward osmosis and seawater reverse osmosis (Algal FO-SWRO) membranes system for potable water reuse and hydrothermal liquefaction (HTL) to produce bioenergy and subsequent nutrients extraction from the harvested algal biomass. The benchmark system includes (ii) an advanced water purification facility (AWPF) that consists of a conventional activated sludge biological treatment (CAS), microfiltration (MF), brackish water reverse osmosis (BWRO), ultraviolet/advanced oxidation process (UV-AOP), and granular activated carbon (GAC), with anaerobic digestion for sludge treatment. Capital expenditures (CAPEX) and operational expenditures (OPEX) were calculated for each unit of both systems (i.e., sub-systems). Based on a 76% overall water recovery designed for the benchmark system, the water cost was estimated at $2.03/m 3 . The highest costs in the benchmark system were found on the CAS and the anaerobic digester, with the UV-AOP combined with GAC for hydrogen peroxide (H 2 O 2 ) quenching as the driving factor in the increased costs of the system. The cost of the main system, based on an overall 88% water recovery, was estimated to be $1.97/m 3 , with costs mostly driven by the FO and SWRO membranes. With further cost reduction and optimization for FO membranes such as membrane cost, water recovery, and flux, the main system can provide a much more economically viable alternative in its application than a typical benchmark system., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

This study investigated the impact of seasonal variation and operating conditions on recovery of potable quality water from municipal wastewater effluent using an integrated algal treatment process with a dual forward osmosis (FO)-reverse osmosis (RO) membrane system. Pilot study of the algal process treating primary effluent validated the technical viability and seasonal performance during warm weather (May to October, 25-55 °C) using an extremophilic algal strain Galdieria sulphuraria, and during cold weather (November to April, 4-17 °C) using polyculture strains of algae and bacteria. Algal effluents from both seasons were used as the feed solution for the laboratory FO-RO study. In addition, pilot-scale FO-RO experiments were conducted to compare the system performance during treatment of algal effluent and secondary effluent from the conventional treatment facility. At 90% water recovery, the FO-RO achieved over 90% overall rejection of major ions and organic matter using the bench-scale system and over 99% rejection of all contaminants in pilot-scale studies. Detailed water quality analysis indicated that the product water from the integrated system met both the primary and secondary drinking water standards. This study demonstrated that the FO-RO system can be engineered as a viable alternative to treat algal effluent and secondary effluent for potable water reuse independent of seasonal variations and operating conditions., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Municipal wastewater is a reliable source from which water, renewable energy, and nutrients could be recovered for beneficial use. Our previous efforts have documented that an innovative algal-based wastewater treatment (WWT) system could recover energy and nutrients from wastewater while having a lower energy footprint than conventional WWT processes. As a biological treatment process, the algal WWT can be affected by algal species, operating conditions, and meteorological factors. This study aimed to identify suitable algal cultures to treat municipal wastewater during warm and cold weather. The algal system achieved the secondary effluent discharge standards for biochemical oxygen demand and nutrients within 2-3 days during warm weather (May to October, 25-55 °C) using an extremophilic algal strain Galdieria sulphuraria; and within 1-2 days in winter (November to April, 4-17 °C) using polyculture strains of algae with bacteria. The impact of seasonal variation and operating conditions on the water quality of pilot-scale algal bioreactors was compared with a full-scale conventional WWT system. The treatment performance of the algal system (NH 4 -N: 1.3 ± 1.25 mg/L in winter and not detected in summer and conventional system; PO 4 -P: 0.89 ± 0.6 mg/L in winter, 0.02 ± 0.03 mg/L in summer and, 5.93 ± 1.32 mg/L in conventional system) was comparable or better than that of the conventional WWT in nutrients removal and other contaminants were below the discharge standards. This study indicates that the algal system can be engineered for reliable wastewater treatment independent of seasonal variations., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Treatment and reuse of produced water (PW), the largest wastewater stream generated during oil and gas production, provides a promising option to address the increasing clean water demands. High-performance treatment technologies are needed to efficiently remove the organic and inorganic contaminants in PW for fit-for-purpose applications. Photocatalytic membrane reactor (PMR) is an emerging green technology for removal of organic pollutants, photoreduction of heavy metals, photo-inactivation of bacteria, and resource recovery. This study critically reviewed the mechanisms of photocatalysis and membrane processes in PMR, factors affecting PMR performance, rational design, and evaluation metrics for PW treatment. Specifically, PW characteristics, photocatalysts properties, membranes applied, and operating conditions are of utmost importance for rational design and reliable operation of PMR. PW pretreatment to remove oil and grease, colloidal and suspended solids is necessary to reduce membrane fouling and ensure optimal PMR performance. The metrics to evaluate PMR performance were developed including light utilization, exergetic efficiency, water recovery, product water improvement, lifetime of the photocatalyst, and costs. This review also presented the research gaps and outlook for future research., (Copyright © 2021 Elsevier B.V. All rights reserved.)

The current technologies to treat hypersaline produced water (PW), such as thermal evaporation, are usually energy-intensive and cost-prohibitive. This study developed a low-cost, robust, solar-driven carbon black and airlaid paper-based evaporator (CAPER) for desalination of PW in the Permian Basin, United States. The study aims to better understand the removal of aromatic organic compounds and heavy metals during solar distillation, water output, and heat transfer. Outdoor experiments using CAPER assisted with polystyrene foam in a single slope, single basin solar still achieved an enhanced average evaporation rate of 2.23 L per m 2 per day, 165% higher than that of a conventional solar still. Analysis of heat transfer models demonstrated that CAPER solar evaporation achieved an evaporative heat transfer coefficient of ∼28.9 W m -2 ·K -1 , 27.9% higher than without CAPER. The maximum fractional energy of evaporation and convection heat transfer inside the solar still with and without CAPER was ∼81.4% and ∼78.2%, respectively. For the PW with a total dissolved solids concentration of 134 g L -1 , solar distillation removed 99.97% salts and over 98% heavy metals. The high removal efficiency of 99.99% was achieved for Ca, Na, Mg, Mn, Ni, Se, Sr, and V. Organic characterization revealed that solar distillation removed over 83% aromatic compounds. Solar desalination using CAPER provides a low-cost and high-performance process to treat PW with high salinity and complex water chemistry for potential fit-for-purpose beneficial uses., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

In this study, the purification and characterization of a novel polysaccharide-based bioflocculant BM2 produced by a bacterium Bacillus megaterium strain PL8 with self-flocculating property were investigated. The results showed that BM2 was an acidic polysaccharide composed of Gal, GalUA, Glc, GlcUA and Man at a molar ratio of 45.1: 33.8:9.3:9.2:2.4, respectively. The molecular weight of BM2 was 4.55 × 10 6  Da. BM2 had high flocculation efficiencies across a wide pH ranged from 4 to 11 and a wide temperature ranged from 20 to 100 °C towards kaolin clay. BM2 was a cation-independent bioflocculant which could achieve high flocculation activity without the addition of other cations. Adsorption bridging was the main mechanism in the flocculation process of BM2 towards kaolin clay. The BM2 also displayed a high removal efficiency in terms of Congo red (88.14%) and Pb 2+ ions (82.64%). These results suggested that BM2 had a great potential as an efficient bioflocculant candidate in wastewater treatment., (Copyright © 2020 Elsevier B.V. All rights reserved.)

A coupled algal-osmosis membrane treatment system was studied for recovering potable-quality water from municipal primary effluent. The core components of the system included a mixotrophic algal process for removal of biochemical oxygen demand (BOD) and nutrients, followed by a hybrid forward osmosis (FO)-reverse osmosis (RO) system for separation of biomass from the algal effluent and production of potable-quality water. Field experiments demonstrated consistent performance of the algal system to meet surface discharge standards for BOD and nutrients within a fed-batch processing time of 2-3 days. The hybrid FO-RO system reached water productivity of 1.57 L/m 2 -h in FO using seawater as draw solution; and permeate flux of 3.50 L/m 2 -h in brackish water RO (BWRO) and 2.07 L/m 2 -h in seawater RO (SWRO) at 2068 KPa. The coupled algal-membrane system achieved complete removal of ammonia, fluoride, and phosphate; over 90% removal of calcium, sulfate, and organic carbon; and 86-89% removal of potassium and magnesium. Broadband characterization using high resolution mass spectrometry revealed extensive removal of organic compounds, particularly wastewater surfactants upon algal treatment. This study demonstrated long-term performance of the FO system at water recovery of 90% and with membrane cleaning by NaOH solution., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Microbial fuel cells (MFCs) are a promising energy-positive wastewater treatment technology, however, the system's cost-effectiveness has been overlooked. In this study, two new anode materials - hard felt (HF) and carbon foam (CF) - were evaluated against the standard graphite brush (GB) to determine if using inexpensive materials with less than ideal properties can achieve more cost-effective treatment than high-cost, high-performing materials. Using domestic wastewater as the substrate, power densities for the GB, HF and CF-MFCs were 393, 339 and 291 mW m(-2) normalized by cathodic surface area, respectively. Higher power densities correlated with larger anodic surface areas and anodic current densities but not with electrical conductivity. Cyclic voltammetry revealed that redox systems used for extracellular electron transport in the GB, HF and CF-MFCs were similar (-0.143 ± 0.046, -0.158 ± 0.004 and -0.100 ± 0.014 V vs. Ag/AgCl) and that the electrochemical kinetics of the MFCs showed no correlation with their respective electrical conductivity. 16S rRNA sequencing showed the GB, HF and CF microbial community compositions were not statistically different while organic removal rates were nearly identical for all MFCs. The HF-MFC generated a power output to electrode cost (W $(-1)) 1.9 times greater than the GB-MFC, despite producing 14% less power and 15% less anodic current, while having 2.6 times less anodic surface area, 2.1 times larger charge transfer resistance and an electrical conductivity three orders of magnitude lower. The results demonstrate that inexpensive materials are capable of achieving more cost-effective treatment than high-performing materials despite generating lower power when treating real wastewater., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Desalination of impaired water can be hindered by the limited options for concentrate disposal. Selective removal of specific contaminants using inexpensive adsorbents is an attractive option to address the challenges of concentrate management. In this study, two types of ferric-based drinking water treatment solids (DWTS) were examined for arsenate removal from reverse osmosis concentrate during continuous-flow once-through column experiments. Arsenate sorption was investigated under different operating conditions including pH, arsenate concentration, hydraulic retention time, loading rate, temperature, and moisture content of the DWTS. Arsenate removal by the DWTS was affected primarily by surface complexation, electrostatic interactions, and arsenate speciation. Results indicated that arsenate sorption was highly dependent on initial pH and initial arsenate concentration. Acidic conditions enhanced arsenate sorption as a result of weaker electrostatic repulsion between predominantly monovalent H2AsO4(-) and negatively charged particles in the DWTS. High initial arsenate concentration increased the driving force for arsenate sorption to the DWTS surface. Tests revealed that the potential risks associated with the use of DWTS include the leaching of organic contaminants and ammonia, which can be alleviated by using wet DWTS or discarding the initially treated effluent that contains high organic concentration., (Copyright © 2015 Elsevier Inc. All rights reserved.)

The rapid development of unconventional oil and gas production has generated large amounts of wastewater for disposal, raising significant environmental and public health concerns. Treatment and beneficial use of produced water presents many challenges due to its high concentrations of petroleum hydrocarbons and salinity. The objectives of this study were to investigate the feasibility of treating actual shale gas produced water using a bioelectrochemical system integrated with capacitive deionization-a microbial capacitive desalination cell (MCDC). Microbial degradation of organic compounds in the anode generated an electric potential that drove the desalination of produced water. Sorption and biodegradation resulted in a combined organic removal rate of 6.4 mg dissolved organic carbon per hour in the reactor, and the MCDC removed 36 mg salt per gram of carbon electrode per hour from produced water. This study is a proof-of-concept that the MCDC can be used to combine organic degradation with desalination of contaminated water without external energy input., (Copyright © 2014 Elsevier B.V. All rights reserved.)

To meet surging water demands, water reuse is being sought as an alternative to traditional water resources. However, contamination of water resources by trace organic compounds (TOrCs), including pharmaceuticals, personal care products, disinfection byproducts, and industrial chemicals is of increasing concern. These compounds are not readily removed by conventional water treatment processes and require new treatment technologies to enable potable water reuse. Forward osmosis (FO) has been recognized in recent years as a robust process suitable for the treatment of highly impaired streams and a good barrier to TOrCs. To date, at least 14 studies have been published that investigated the rejection of various TOrCs by FO membranes under a variety of experimental conditions. In this paper, TOrC rejection by FO has been critically reviewed, evaluating the effects of membrane characteristics and orientation, experimental scale and duration, membrane fouling, feed solution chemistry, draw solution composition and concentration, and transmembrane temperature on process performance. Although it is important to continue to investigate the removal of diverse TOrCs by FO, and especially with new FO membranes, it is critically important to adhere to standard testing conditions to enable comparison of results between studies. Likewise, feed concentration of TOrCs during FO testing must be environmentally relevant (most commonly 10-100 ng/L range for most wastewaters) and not excessively high, and in addition to testing TOrC rejection in clean feedwater, the effects of real water matrix and membrane fouling on TOrC rejection must be evaluated.

Concentrate disposal and management is a considerable challenge for the implementation of desalination technologies, especially for inland applications where concentrate disposal options are limited. This study has focused on selective removal of arsenic and monovalent ions from brackish groundwater reverse osmosis (RO) concentrate for beneficial use and safe environmental disposal using in situ and pre-formed hydrous ferric oxides/hydroxides adsorption, and electrodialysis (ED) with monovalent permselective membranes. Coagulation with ferric salts is highly efficient at removing arsenic from RO concentrate to meet a drinking water standard of 10 μg/L. The chemical demand for ferric chloride however is much lower than ferric sulfate as coagulant. An alternative method using ferric sludge from surface water treatment plant is demonstrated as an efficient adsorbent to remove arsenic from RO concentrate, providing a promising low cost, "waste treat waste" approach. The monovalent permselective anion exchange membranes exhibit high selectivity in removing monovalent anions over di- and multi-valent anions. The transport of sulfate and phosphate through the anion exchange membranes was negligible over a broad range of electrical current density. However, the transport of divalent cations such as calcium and magnesium increases through monovalent permselective cation exchange membranes with increasing current density. Higher overall salt concentration reduction is achieved around limiting current density while higher normalized salt removal rate in terms of mass of salt per membrane area and applied energy is attained at lower current density because the energy unitization efficiency decreases at higher current density., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Forward osmosis (FO) is an emerging membrane separation process that continues to be tested and implemented in various industrial water and wastewater treatment applications. The growing interests in the technology have prompted laboratories and manufacturers to adopt standard testing methods to ensure accurate comparison of membrane performance under laboratory-controlled conditions; however, standardized methods might not capture specific operating conditions unique to industrial applications. Experiments with cellulose triacetate (CTA) and polyamide thin-film composite (TFC) FO membranes demonstrated that hydraulic transmembrane pressure (TMP), common in industrial operation of FO membrane elements, could affect membrane performance. Experiments were conducted with three FO membranes and with increasing TMP up to a maximum of 50 psi (3.45 bar). The feed solution was a mixture of salts and the draw solution was either a NaCl solution or concentrated seawater at similar osmotic pressure. Results revealed that TMP minimally affected water flux, reverse salt flux (RSF), and solute rejection of the CTA membrane. However, water flux through TFC membranes might slightly increase with increasing TMP, and RSF substantially declines with increasing TMP. It was observed that rejection of feed constituents was influenced by TMP and RSF.

Microbial desalination cell represents a new technology for simultaneous wastewater treatment, water desalination, and energy production. This study characterized the long-term performance of MDC during wastewater treatment and identified the key factors that caused performance decline. The 8-month operation shows that MDC performance decreased over time, as indicated by a 47% decline in current density, a 46% drop in Columbic efficiency, and a 27% decrease in desalination efficiency. Advanced electrochemical, microscopy, and spectroscopy analyses all confirmed biofouling on the anion exchange membrane, which increased system resistance and reduced ionic transfer and energy conversion efficiency. Minor chemical scaling was found on the cation exchange membrane surface. Microbial communities became less diverse at the end of operation, and Proteobacteria spp. was dominant on both anode and AEM fouling layer surface. These results provide insights into the viability of long-term MDC operation on reactor performance and direct system development through membrane optimization., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The low conductivity and alkalinity in municipal wastewater significantly limit power production from microbial fuel cells (MFCs). This study integrated desalination with wastewater treatment and electricity production in a microbial desalination cell (MDC) by utilizing the mutual benefits among the above functions. When using wastewater as the sole substrate, the power output from the MDC (8.01 W/m(3)) was four times higher than a control MFC without desalination function. In addition, the MDC removed 66% of the salts and improved COD removal by 52% and Coulombic efficiency by 131%. Desalination in MDCs improved wastewater characteristics by increasing the conductivity by 2.5 times and stabilizing anolyte pH, which therefore reduced system resistance and maintained microbial activity. Microbial community analysis revealed a more diverse anode microbial structure in the MDC than in the MFC. The results demonstrated that MDC can serve as a viable option for integrated wastewater treatment, energy production, and desalination., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Forward osmosis (FO) is a membrane separation technology that has been studied in recent years for application in water treatment and desalination. It can best be utilized as an advanced pretreatment for desalination processes such as reverse osmosis (RO) and nanofiltration (NF) to protect the membranes from scaling and fouling. In the current study the rejection of trace organic compounds (TOrCs) such as pharmaceuticals, personal care products, plasticizers, and flame-retardants by FO and a hybrid FO-RO system was investigated at both the bench- and pilot-scales. More than 30 compounds were analyzed, of which 23 nonionic and ionic TOrCs were identified and quantified in the studied wastewater effluent. Results revealed that almost all TOrCs were highly rejected by the FO membrane at the pilot scale while rejection at the bench scale was generally lower. Membrane fouling, especially under field conditions when wastewater effluent is the FO feed solution, plays a substantial role in increasing the rejection of TOrCs in FO. The hybrid FO-RO process demonstrated that the dual barrier treatment of impaired water could lead to more than 99% rejection of almost all TOrCs that were identified in reclaimed water.

Capacitive deionization (CDI) with carbon-aerogel electrodes represents a novel process in desalination of brackish water and has merit due to its low fouling/scaling potential, ambient operational conditions, electrostatic regeneration, and low voltage requirements. The objective of this study was to investigate the viability of CDI in treating brackish produced water and recovering iodide from the water. Laboratory- and pilot-scale experiments were conducted to identify ion selectivity, key operational parameters, evaluate desalination performance, and assess the challenges for its practical applications. The performance of the CDI technology (CDT) system tested was consistent throughout the laboratory- and field-scale experiments. Deterioration of the carbon-aerogel electrodes was not observed during testing. The degree of ions adsorbed to the carbon aerogel (in mol/g aerogel) during treatment of brackish water was dependent upon initial ion concentrations in the feed water with the following selectivity I>Br>Ca>alkalinity>Mg>Na>Cl. The preferential sorption of iodide revealed merit to efficiently recover iodide from brackish water even in the presence of dominant co-ions. The research findings derived from this study identified parameters that merit further improvements regarding design and operation, including modification of pore-size distribution of aerogel, development of high capacitance and low-cost electrode materials, reducing the dead volume after regeneration and rinsing, minimizing energy consumption, and maximizing system recovery.

The rejection of emerging trace organics by a variety of commercial reverse osmosis (RO), nanofiltration (NF), and ultra-low-pressure RO (ULPRO) membranes was investigated using TFC-HR, NF-90, NF-200, TFC-SR2, and XLE spiral membrane elements (Koch Membrane Systems, Wilmington, Massachusetts) to simulate operational conditions for drinking-water treatment and wastewater reclamation. In general, the presence of effluent organic matter (EfOM) improved the rejection of ionic organics by tight NF and RO membranes, as compared to a type-II water matrix (adjusted by ionic strength and hardness), likely as a result of a decreased negatively charged membrane surface. Rejection of ionic pharmaceutical residues and pesticides exceeded 95% by NF-90, XLE, and TFC-HR membranes and was above 89% for the NF-200 membrane. Hydrophobic nonionic compounds, such as bromoform and chloroform, exhibited a high initial rejection, as a result of both hydrophobic-hydrophobic solute-membrane interactions and steric exclusion, but rejection decreased significantly after 10 hours of operation because of partitioning of solutes through the membranes. This resulted in a partial removal of disinfection byproducts by the RO membrane TFC-HR. In a type-II water matrix, the effect of increasing feed water recoveries on rejection of hydrophilic ionic and nonionic compounds was compound-dependent and not consistent for different membranes. The presence of EfOM, however, could neutralize the effect of hydrodynamic operating condition on rejection performance. The ULPRO and tight NF membranes were operated at lower feed pressure, as compared to the TFC-HR, and provided a product water quality similar to a conventional RO membrane, regarding trace organics of interest.

The incomplete rejection of certain pesticides, disinfection by-products, endocrine disrupting compounds, and pharmaceutically active compounds has been reported during full- and pilot-scale high-pressure membrane applications. Since the removal of these compounds in water and wastewater treatment applications is of great importance where a high product water quality is desired, an understanding of the factors affecting the permeation of solutes in high-pressure membrane systems is needed. In this paper, findings of a comprehensive literature review are reported, targeting membrane rejection mechanisms and factors affecting rejection. The following key solute parameters were identified to primarily affect solute rejection: molecular weight (MW), molecular size (length and width), acid disassociation constant (pKa), hydrophobicity/hydrophilicity (log Kow), and diffusion coefficient (Dp). Key membrane properties affecting rejection that were identified include molecular weight cut-off, pore size, surface charge (measured as zeta potential), hydrophobicity/hydrophilicity (measured as contact angle), and surface morphology (measured as roughness). In addition, feed water composition, such as pH, ionic strength, hardness, and the presence of organic matter, was also identified as having an influence on solute rejection. From the knowledge gained during the literature review, a rejection diagram was proposed, which qualitatively allows prediction of solute rejection if certain solute and membrane properties are known.

Wastewater disinfection by ozone was investigated at pilot scale on different wastewater effluents. Variations in operating conditions showed that a very low hydraulic retention time (2 min) was sufficient for efficient fecal coliform inactivation, provided a sufficient ozone dose was transferred to the effluent. Therefore, the transferred ozone dose appeared to be the critical parameter for the design of wastewater disinfection. As a consequence, the "Ct" approach commonly applied in drinking water treatment should not be used for wastewater ozonation. Design parameters of ozonation were proposed for two types of regulations, and for effluents of different qualities. It was demonstrated that only with an efficient filtration step one can meet stringent standards such as the California Title 22 criteria. In all cases, viruses were totally inactivated; consequently, viruses do not constitute a limiting factor in wastewater disinfection by ozone. The standard drinking water model failed to match the experimental data obtained on real wastewater effluents. A modified approach was successfully developed, based on the simultaneous consumption of ozone by the microorganisms and the organic matrix.

This study explores the effects of alternating current-induced electromagnetic field (EMF) on mitigating brackish water irrigation and soil salinization impacts. Greenhouse experiments were conducted to evaluate the effect of EMF on plant growth, soil properties, and leaching of ions under different conditions, including using brackish water and desalinated water for irrigation and soil compost incorporation. The experiment was performed with four types of irrigation water using soil columns representing field soil layers. EMF-treated brackish water maintained a sodium adsorption ratio of 2.7 by leaching Na+ from the soil. EMF-treated irrigation columns showed an increase in soil organic carbon by 7% over no EMF-treated columns. Compost treatment reduced the leaching of NO3− from the soil by more than 15% using EMF-treated irrigation water. EMF-treated brackish water and compost treatment enhanced plant growth by increasing wet weight by 63.6%, dry weight by 71.4%, plant height by 22.8%, and root length by 115.8% over no EMF and compost columns. EMF-treated agricultural water without compost also showed growth improvements. The findings suggest that EMF treatment, especially combined with compost, offers an effective, low-cost, and eco-friendly solution to mitigate soil salinization, promoting plant growth by improving nutrient availability and soil organic carbon. [ABSTRACT FROM AUTHOR]

The oil and gas (O&G) industry has expanded significantly and brought to the surface large volumes of saline water called produced water (PW), which comprises of underground formation water, injection water, and chemical additives used during extraction and production. PW is traditionally managed via injection wells, evaporation/seepage pits, or recycling for on-site operations. There is increasing interest in PW treatment and reuse outside O&G fields due to freshwater scarcity and concerns about seismic events linked to deep-well injection. Adopting treated PW for reuse outside the O&G sector needs to address the challenges of complex water chemistry, limited toxicity data, and knowledge gaps for appropriate regulatory responses, including risk assessment frameworks on human health and the environment, socio-technical–economic assessments of treatment and reuse applications, and long-term demonstrations and monitoring of fit-for-purpose reuse. This opinion paper proposes a holistic, state-of-the-science pathway for PW treatment, management, and fit-for-purpose reuse outside O&G fields. • Current applications of PW treatment and reuse in the United States are studied. • Opportunities for broad PW reuse inside and outside O&G fields are emphasized. • Regulatory framework and risk assessment approaches for PW reuse are reviewed. • Challenges impeding PW reuse outside O&G fields are discussed. • Human health and environmental risk assessment framework is proposed. [ABSTRACT FROM AUTHOR]

Electro-driven separation processes offer several potential advantages over pressure-driven separation processes such as reverse osmosis for water reuse and desalination, including energy savings for low-salinity waters, cation or anion selectivity, and versatility for fit-for-purpose treatment. In this perspective, we review technologies for electro-driven separation processes and evaluate their prospect for marginalized water sources and fit-for-purpose water treatment, which include improving freshwater sustainability, protecting environmental flows, and improving recycling of industrial process streams and municipal wastewater reuse. We discuss critical aspects related to application, implementation, and techno-economic evaluation of electro-driven separation technologies. Electro-driven processes provide viable options to enhance a circular water economy by reducing salinity and selectively separating contaminants while recovering valuable products with increased environmental sustainability. • Tandem electro-driven separation processes are ideal for tailored desalination. • Selective membranes offer energy-efficient ion removal or recovery opportunities. • Electro-driven processes for brine management enable more sustainable desalination. [ABSTRACT FROM AUTHOR]

Desalination of seawater, brackish water, and reclaimed water is increasingly utilized worldwide to augment and diversify fresh water sources. The lack of economically and ecologically feasible concentrate management options, however, is a major barrier to widespread implementation of desalination, in particular at inland sites. This paper critically reviews strategies and technologies for concentrate management, including disposal, treatment, and beneficial use. Development of energy-efficient, cost-effective, and environmentally benign concentrate management systems is critical if desalination is to become a major part of a sustainable water future. This paper examines the limitations and advantages of a range of concentrate management tools, including emerging and novel technologies for minimization of concentrate volume, enhancement of water recovery, removal of organic contaminants, and recovery of valuable products and energy. [ABSTRACT FROM AUTHOR]

Produced water is the largest byproduct of oil and gas production. Due to the complexity of produced water, especially dissolved petroleum hydrocarbons and high salinity, efficient water treatment technologies are required prior to beneficial use of such waste streams. Photocatalysis has been demonstrated to be effective at degrading recalcitrant organic contaminants, however, there is limited understanding about its application to treating produced water that has a complex and highly variable water composition. Therefore, the determination of the appropriate photocatalysis technique and the operating parameters are critical to achieve the maximum removal of recalcitrant compounds at the lowest cost. The objective of this review is to examine the feasibility of photocatalysis-involved treatment for the removal of contaminants in produced water. Recent studies revealed that photocatalysis was effective at decomposing recalcitrant organic compounds but not for mineralization. The factors affecting decontamination and strategies to improve photocatalysis efficiency are discussed. Further, recent developments and future research prospects on photocatalysis-derived systems for produced water treatment are addressed. Photocatalysis is proposed to be combined with other treatment processes, such as biological treatments, to partially reduce total organic carbon, break down macromolecular organic compounds, increase biodegradability, and reduce the toxicity of produced water. [ABSTRACT FROM AUTHOR]

Produced water is the largest volume of waste product generated during oil and natural gas exploration and production. The traditional method to dispose of produced water involves deep well injection, but this option is becoming more challenging due to high operational cost, limited disposal capacity, and more stringent regulations. Meanwhile, large volumes of freshwater are used for hydraulic fracturing. The goal of this study is to develop cost-effective technologies, and optimize system design and operation to treat highly saline produced water (120–140 g/L total dissolved solids) for hydraulic fracturing. Produced water was collected from a salt water disposal facility in the Permian Basin, New Mexico. Chemical coagulation (CC) using ferric chloride and aluminum sulfate as coagulants was compared with electrocoagulation (EC) with aluminum electrodes for removal of suspended contaminants. The effects of coagulant dose, current density, and hydraulic retention time during EC on turbidity removal were investigated. Experimental results showed that aluminum sulfate was more efficient and cost-effective than ferric chloride for removing turbidity from produced water. The optimal aluminum dose was achieved at operating current density of 6.60 mA/cm2 and 12 min contact time during EC treatment, which resulted in 74% removal of suspended solids and 53–78% removal of total organic carbon (TOC). The energy requirement of EC was calculated 0.36 kWh/m3 of water treated. The total operating cost of EC was estimated $0.44/m3 of treated water, which is 1.7 or 1.2 times higher than CC using alum or ferric chloride as the coagulant, respectively. The EC operating cost was primarily associated with the consumption of aluminum electrode materials due to faradaic reactions and electrodes corrosions. EC has the advantage of shorter retention time, in situ production of coagulants, less sludge generation, and high mobility for onsite produced water treatment. The fine particles and other contaminants after coagulation were further treated in continuous-flow columns packed with different filter media, including agricultural waste products (pecan shell, walnut shell, and biochar), and new and spent granular activated carbon (GAC). Turbidity, TOC, metals, and electrical conductivity were monitored to evaluate the performance of the treatment system and the adsorption capacities of different media. Biochar and GAC showed the greatest removal of turbidity and TOC in produced water. These treatment technologies were demonstrated to be effective for the removal of suspended constituents and iron, and to produce a clean brine for onsite reuse, such as hydraulic fracturing. [ABSTRACT FROM AUTHOR]

A series of TiO 2 -reduced graphene oxide (rGO) coated side-glowing optical fibers (SOFs) were synthesized by polymer assisted hydrothermal deposition method (PAHD), and characterized by crystallographic and spectroscopic methods. Fourier transform infrared spectroscopy showed that the mixed graphene dioxide (GO) was reduced during PAHD coating of TiO 2 -GO nanocomposites. X-ray diffraction patterns revealed TiO 2 presented as a mixture phase of anatase, rutile and brookite in the TiO 2 -rGO nanocomposites. UV–vis absorption spectra of TiO 2 -rGO nanocomposites indicated that mixing rGO into TiO 2 particles could reduce band gap energy, thereby enhancing utilization efficiency of visible light. Photocatalytic performance of the synthesized nanocomposites was measured by the degradation of three pharmaceuticals under UV and visible light irradiation, including carbamazepine, ibuprofen, and sulfamethoxazole. TiO 2 -rGO nanocomposites exhibited significantly higher photocatalytic activities as compared to pure TiO 2 , and were strongly affected by the amount of rGO in the catalysts. While photocatalysis with 2.7% rGO achieved 54% degradation of carbamazepine, 81% of ibuprofen, and 92% of sulfamethoxazole after 180 min UV irradiation, the mineralization rates of the pharmaceuticals were similar between 52% and 59%. The photocatalytic oxidation of pharmaceuticals by the prepared nanocomposites followed the Langmuir–Hinshelwood kinetic model. There was an obvious positive correlation between degradation rate constant and quantum flux for both UV and visible light, with correlation coefficient of 0.991. In addition, long-term photoactivity testing of TiO 2 -rGO coated SOFs demonstrated the durability of the immobilized TiO 2 -rGO nanocomposites on optical fibers for water treatment. [ABSTRACT FROM AUTHOR]

The management of produced water (PW) generated during oil and gas operations requires effective treatment and comprehensive chemical and toxicological assessment to reduce the environmental risks associated with reuse or discharge. This study evaluated a treatment train that included a low-temperature thermal distillation pilot system followed by granular activated carbon (GAC) and zeolite post-treatment for processing hypersaline Permian Basin PW. Our study provides a unique and comprehensive assessment of the treatment efficiency considering a targeted chemical scheme together with whole effluent toxicity (WET) tests across four trophic levels regarding aquatic critical receptors of concern (ROC): Raphidocelis subcapitata , Vibrio fischeri , Ceriodaphnia dubia, and Danio rerio. The distillate from the thermal distillation process met various numeric discharge standards for salinity and major ions. However, it did not meet toxicity requirements established by the United States National Pollutant Discharge Elimination System program. Subsequent post-treatment using GAC and zeolite reduced the concentration of potential stressors, including volatile organics, NH 3 , Cd, Cr, Zn, and Mn in the final effluent to below detection limits. This resulted in a consistent toxicity reduction across all WET tests, with no observable adverse effects for R. subcapitata, C. dubia, and D. rerio (no observed effect concentration >100%), and V. fischeri effects reduced to 19%. This study realizes the feasibility of treating PW to non-toxic levels and meeting reuse and discharge requirements. It underscores the importance of implementing integrated treatment trains to remove the contaminants of concern and provides a systematic decision framework to predict and monitor environmental risks associated with PW reuse. [Display omitted] • GAC and zeolite reduced most VOCs and ammonia to levels below detection limits. • Removal of potential chemical stressors was consistent with toxicity reductions. • WET tests indicated thermal distillation-GAC-zeolite treated PW to non-toxic levels. • NPDES numeric & narrative criteria were used to assess treated PW discharge risks. [ABSTRACT FROM AUTHOR]

Abstract: To produce large volumes of newly discovered unconventional gas, hydraulic fracturing of wells is commonly practiced in basins where shale gas and coal bed methane are extracted. Hydraulic fracturing of wells during oil and gas (O&G) exploration consumes large volumes of fresh water and generates larger volumes of contaminated wastewater. In this study, a novel application of forward osmosis (FO) was tested for treatment and reclamation of water from drilling waste to facilitate beneficial water reuse. By using FO, two major benefits were achieved: both the volume of the waste stream and the need for a fresh water source were greatly reduced. Results indicate that FO can achieve high rejection of organic and inorganic contaminants, membrane fouling was reversible, and that the process was able to effectively recover more than 80% of the water from the drilling waste. Osmotic backwashing was demonstrated to be an effective membrane cleaning technique; successfully removing fouling and restoring water flux. [Copyright &y& Elsevier]

• Nanocomposite cation-exchange membranes were developed for organic fouling control. • The nanocomposite membranes showed superior antifouling and desalination capacity. • All modified membranes did not show any acute toxicity towards Vibrio fischeri. Organic fouling hinders the application of membrane treatment of alternative water. In this study, polyethyleneimine (PEI), titanium dioxide (TiO 2) nanoparticles, and graphene oxide (GO) nanosheets were used for modifying cation-exchange membranes to enhance anti-organic fouling and desalination performance during electrodialysis of synthetical water and municipal wastewater. Fouling propensity of the unmodified and modified membranes was quantitatively evaluated by measuring organic accumulation on membrane surface using humic acid (HA, simulating natural organic matter) and bovine serum albumin (BSA, simulating organic matter in municipal wastewater effluent) as model foulants. Significant surface deposition of HA was observed on the unmodified, PEI-TiO 2 , and PEI-modified membrane surfaces while trivial HA fouling was detected on the PEI-GO membrane. BSA fouling was minor for all the modified membranes compared to the unmodified membrane. Desalination efficiency of electrodialysis with the modified membranes, except the PEI-modified membrane, was significantly improved in treating synthetical water with HA foulant compared to the electrodialysis with the unmodified membrane (20%~40% reduction of normalized salt removal). Relatively stable desalination behaviors were observed for each membrane system in treating BSA-containing synthetical water, and enhanced desalination was demonstrated with the modified membranes. Subsequent long-term fouling experiments with wastewater effluent revealed the superior antifouling capacity of the nanocomposite membranes (especially for the PEI-GO membrane) over 100-hour operation, while the unmodified membranes exhibited severe fouling (with total more than 60% decline of normalized salt removal) after approximately 50-hour treating wastewater. In a standard Microtox® acute toxicity assay, the nanocomposite membranes did not show any acute toxicity towards Vibrio fischeri due to potential leaching of PEI and nanomaterials, indicating safe utilization of the modified membranes for water treatment. [ABSTRACT FROM AUTHOR]

Membrane fouling, in particular biofouling is a major problem in membrane applications for water and wastewater treatment. In this study, cation-exchange membranes were modified with conductive polymer polyethyleneimine and nanomaterials such as titanium dioxide (TiO 2) and graphene oxide (GO) to improve membrane anti-microbial properties and energy efficiency during electrodialysis. The anti-fouling potential was evaluated by quantitative measurement of biomass and biofilm accumulation on membrane surface with Escherichia coli (E. coli) as model microbes. Experimental results showed polyethyleneimine and nanomaterials coating changed membrane surface hydrophilicity and significantly improved anti-biofouling properties with an optimal nanomaterial dosage of 37.5 μg/mL of coating solution. Polyethyleneimine had limited effect on preventing microbial cell attachment, but demonstrated remarkable anti-biofilm growth by its cytotoxicity. Overall desalination performance of polyethyleneimine coated membrane was similar to unmodified membrane. GO coating significantly improved desalination efficiency because of its high conductivity and negative charge, while TiO 2 coated membrane showed decreased overall desalination performance due to its reduced electrical conductivity. Image 1 • Anti-biofouling and energy-efficient cation exchange membranes were developed. • Polyethyleneimine (PEI) reduced biofilm by 67% but not cell attachment. • PEI-TiO 2 coating reduced cell attachment and biofilm coverage by 60% and 78%. • PEI-GO coating reduced cell attachment and biofilm coverage by 96% and 98%. • PEI-GO coating significantly enhanced energy efficiency during electrodialysis. [ABSTRACT FROM AUTHOR]

• Struvite recovery from produced water was investigated for the first time. • Calcium pretreatment by Na 2 CO 3 achieved low Mg2+ loss and high Ca2+ removal. • High-purity struvite was obtained under Mg/N/P molar ratio = 1.5:1:1.5 & pH = 9.5. • Struvite precipitate was free of heavy metals and organic contaminants. • High toxicity reduction towards Vibrio fischeri (60%) was observed. Unconventional oil and gas industries generate huge amounts of produced water (PW) containing high concentrations of potentially hazardous organic and inorganic contaminants. This study demonstrated the feasibility of simultaneously recovering NH 4 +, K+ and Mg2+ from PW by struvite precipitation after calcium pretreatment with Na 2 CO 3 addition or CO 2 stripping. Without pretreatment, calcium exhibited strong competition for phosphate through the formation of Ca 3 (PO 4) 2 precipitate. The pretreatment with a Ca2+:CO 3 2− molar ratio of 1:1.2 achieved a relatively low loss rate of Mg2+ (31.3%) and high Ca2+ removal efficiency (95.9%). The results also revealed that the Mg/N/P molar ratio and solution pH had a remarkable effect on the struvite precipitation, while the seeding dosage and Na+ slightly influenced struvite formation. The combination of pH = 9.5 & Mg/N/P molar ratio = 1.5:1:1.5 was ideal for struvite recovery from PW, resulting in NH 4 +, K+ and Mg2+ recovery efficiencies of 85.9%, 24.8% and 96.8%, respectively. The results of X-ray diffraction and scanning electron microscopy further confirmed that the precipitates generated at this optimal condition were orthorhombic struvite. Moreover, along with the struvite recovery, no accumulation of heavy metals and organic contaminants was observed, indicating that the struvite quality was sufficient for field application. Furthermore, struvite recovery process was able to reduce the Microtox toxicity of PW towards Vibrio fischeri by 60%. Considering the low cost and relatively simple technology, struvite precipitation process has the potential to be used for large-scale applications for produced water treatment and resource recovery. [ABSTRACT FROM AUTHOR]